1. Field of the Invention
The present invention relates to a printing press and more particularly a structure of a printing section disposed between a sheet feeding section and a sheet discharge section so as to supply a printing plate to a clamping gripper that is disposed on a plate cylinder and to mount the supplied printing plate on the plate cylinder.
2. Related Art
A sheet-fed printing press (hereinafter referred simply to a printing press) generally includes a printing section between a sheet feeding section and a sheet discharge section. This printing section is to print on sheets by a printing plate mounted on a plate cylinder. There is a necessity to mount a printing plate on the plate cylinder with accurate alignment. For mounting a printing plate on the plate cylinder, the printing press is generally equipped with a printing plate mounting device that automatically mounts a printing plate, which has been manually inserted into a clamping gripper disposed in the plate cylinder. According to a recently proposed printing press, an automatic supply mechanism is employed to automatically supply a printing plate (a new plate), which has been once set at a predetermined position by an operator, to a clamping gripper. For example, Japanese Patent No. 2844231 proposes an automatic plate supply device that has a sucker arranged on a printing plate guide plate disposed on the front side of a body cover of the printing section for sucking a printing plate (plate rear side). According to a technique of this Patent, the printing plate guide plate with the printing plate held by the sucker is inclined towards the clamping gripper of the plate cylinder and the sucker is linearly moved towards the clamping gripper so as to supply the printing plate to the clamping gripper.
Meanwhile, in supplying each printing plate to the clamping gripper, the printing plate is brought into alignment with the clamping gripper (plate cylinder) by the engagement between a pair of axially spaced apart protrusions as an engaging means formed on the clamping gripper and cutouts as an engaged means formed in each printing plate. In this arrangement, the sucker holds by suction a printing plate which has been laid down on the printing plate guide plate and moves towards the clamping gripper while holding the printing plate. If the printing plate on the printing plate guide plate is axially displaced relative to a given position, the engaged means of the printing plate is unlikely to be in alignment with the engaging means so that, with the printing press of this type, which automatically drives the clamping gripper, a signal generated upon the alignment of a printing plate with the plate cylinder is not output, and hence the clamping gripper cannot be controlledly driven. This makes it impossible to mount the printing plate on the plate cylinder. In order to address this problem, for example, Japanese Utility Model Application Laid-open No. Hei-05-26374 proposes a technique in which a guide piece is arranged on the printing plate guide plate for guiding a printing plate along a lateral side edge thereof so as to bring the engaged means of the printing plate into alignment with the engaging means of the clamping gripper. For achieving this alignment in the printing press of this type, the plate cylinder must be previously returned to a given axial position (original point) proper for a printing plate to be newly supplied, as described in for example Japanese Patent No. 3066614. The returning of a plate registration (the axial position) of the plate cylinder to the original point (position) is required for the reason that if the plate registration (the axial position) of the plate cylinder has been displaced from a proper position after the use of the printing plate for the last printing operation, a newly supplied printing plate for the subsequent printing operation may not match the plate registration (the axial position of the plate cylinder), and as a result, it is not possible to bring the cutouts as the engaged means of the printing plate into engagement with the protrusions as the engaging means of the clamping gripper.
The above conventional printing press is provided with a guide piece arranged on the printing plate guide plate so as to guide a lateral edge of the supplied printing plate. This guide piece is fixed in position on the printing plate guide plate and therefore, if the mounting position of the printing plate guide plate relative to the body cover is not accurate, the alignment of the engaged means with the engaging means may not be possible. Also, as another disadvantage associated with the prior art, it is necessary to perform an additional step of returning the plate registration (axial position) of the plate cylinder to the original point (position) in order to make the cutouts as the engaged means match with the protrusions as the engaging means of the clamping gripper of the plate cylinder.
It is an object of the present invention to provide a printing press that is capable of accurately bringing a printing plate into alignment with the plate cylinder by securely making the engaged means of the printing plate match in position with the engaging means provided on the side of the plate cylinder in supplying the printing plate to the plate cylinder, as well as omitting the necessity to return the plate registration of the plate cylinder to the original point.